Blue printing



Patented Sept. 13, 1932 UNITED STATES ROBERT E. KWEGH, OF CHICAGO,ILLINOIS BLUE PRINTING No Drawing.

The present invention relates to the art of image reprmluction throughthe action of lighton iron salts, and has particular refereuce to animproved process by which image reproduction in blue printing, blue lineprinting and the like is facilitated.

The art of blue printing is based on the reducing action of light uponchemical compounds such as ferric salts, and the final in'iage is formeddirectly from the reduction product. Of necessity, then, the density ofthe image is dependent upon the amount of reduction product present.

A primary object of my invention is to provide a blue printing orsimilar process which will produce reproductions more permanent to lightand washing than processes known heretofore.

Another objectis to improve the brillianceof reproductimis obtained fromlight-sensitive paper prepared from iron salt-s.

A further object is to provide an improved process for utilizinglight-sensitive paper of the character described which has been over orunder exposed.

A still further object is to improve the fastness of color of an imageformed upon paper coated with iron salts, when the same is treated withwater, that is, to prevent bleeding of the print.

These and other objects will become apparent from the followingdescription The invention will be described with particular reference toblue, printing. and it is to be understood that this description is forpurposes of illustration and explanation.

Blue print paper is customarily prepared by coating :1 suitable type ofpaper with a ferric salt, such as ferric ammonium citrate or oxalate,which will be reduced by the action of light to the ferrous state. Withthe ferric salt is admixed a second compound which combines with thereduced iron compound to form a highly colored image. It is customary toemploy potassium ferricyanide for this purpose.

A. diagram, the reproduction of which is desired, is transposed over thecoated paper, and then exposed to the action of actinic lightApplication filed August 911, 1931. Serial No. 560,507.

for a period of time sufficient to insure reduction of the ferricammonium citrate.

Upon washing the exposed paper with water, the ferrous salt combineswith the potassium ferricyanide to form"lurnbulls blue, and theunexposed and unreduced ferric annnonium citrate is dissolved out of thepaper.

In some cases, it is desirable to dissolve the potassium ferricyanide inthe wash liquid rather than to coat the paper with the same.

After being washed with water, the exposed paper is ordinarily washed ina bath of an oxidizing agent such as potassium dichromate, again washedwith Water, and dried. a

In accordance with my invention, before being washed with water, theexposed paper is subjected to a bath containing a neutral or alkalinesolution of a ferrocyanide reducing agent capable of intensifying theimage. \Vhile it is preferred to employ potassium ferroc \-'anide, othercompmmds, such as ammonium ferrocyanide, sodium ferrocyanide, andcalcium ferrocyanide. may also be. used.

I have found that considerably more desirable results are obtained whenthe solution is alkaline, for example, having a pH of 8 or more. Sodiumcarbonate or other alkaline compound may be employed to impart thedesired alkalinity.

With the potassium ferrocyanide bath is combined a stronger reducingagent or inhibitor such as sodium hyposulfitc, sodium sultite, orpotassium meta bisulfite. The amount of inhibitor will depend upon thelength of time between the intensifying bath and the oxidizing bath towhich the paper is later subjected.

Subsequent to the intensifying bath, the paper is subjected to a waterbath and an oxidizing bath as described heretofore with reference to theprior art.

To illustrate my invention the following specific example is given.

A photo sensitive base is prepared by coating paper, cloth or somesimilar carrier with a 16 percent solution of ferric ammonium citrate, a16 percent solution of potassium ferricyanide, and a- 5 percent solutionof oxalic acid. The paper prepared in this manner is exposed beneath thedesired diagram to light.

After exposure the paper is subjected to an intensifying solutioncomposed of an 18 percent solution of potassium ferrocyanide to which isadded 1 ercent sodium carbonate and approximate y 3 percent sodlumsulfite.

The intensified paper is then washed with water, and immersed in a 7 percent solution color obtained, and, equally important, elim-.

of'potassium dichromate.

Following the oxidizing bath, the paper is again washed with water, anddried.

As evidenced upon operation of my improved process, the washing withpotassium ferrocyanide increases the permanence of the inates what isknown in the art as bleeding. Various appllcatlons and variations of myinvention will occur to one skilled in the art,

paper to the action of light modified by. a

design, and intensifying the exposed paper by treatment with an alkalinesolution of potassium ferrocyanide.

2. A process of printing, which comprises providing a photo-sensitizedsheet of paper prepared with a light-reducible ferric salt and aferricyanide compound, transposing thereover an opaque diagram, exposingsai paper to the action of light, and intensifying the exposed paper bytreatment with an alkaline solution of potassium ferrocyanide and areducing agent which will inhibit oxidation of ferrous compounds.

3. In the process of blue printing, the step which vcomprises subjectingexposed blue print paper photochemically prepared with a light-sensitiveferric compound and a ferricyanide compound to treatment with an alka-'line solution of potassium ferrocyanide.

4. In the process of printing images upon paper photo-sensitized with alight-sensitive ferric compound and potassium ferricyanide, the step ofsubjecting the exposed paper to the action of an alkaline solutioncontaining potassium ferrocyanide and sodium sulfite.

5. In the process of printing images upon paper photo-sensitized with alight-sensitive ferric compound and a ferricyanide compound, the stepsof treating the exposed paper with an alkaline solution containingpotassium ferrocyanide and then subjecting the paper to treatment withan oxidizing agent capable of developing an image thereon.

6. In the process of printing images upon paper photo-sensitized with alight-sensitive ferrlc compound, an organicacid, and a ferricyanidecompound, the step of treating the exposed paper with an alkalinesolution containing potassium ferrocyanide and a compound from the groupcomprising sodium sulfite, sodium hyposulfite, and sodium metabisulfite. y

7. A process of printing, which comprises providing a sheet of paperphoto-sensitized by a light-reducible ferric compound,.and aferricyanide compound, transposing thereover an opaque diagram, exposingthe paper to light, subjecting theexposed paper to the action of analkaline solution of a ferrocyanide compound capable of intensifying thecolor of the exposed portion of said paper and a reducing agent capableof inhibiting the oxidation of ferrous compounds, washing said paperwith water, and then treating the washed paper with an oxidizing agentcapable of developing the exposed portions of said paper.

8. A process of printing, whichcomprises providing a sheet of papercoated with a light-sensitive ferric compound, an organic acid, andpotassium ferricyanide, transposing thereover a diagram, exposingthepaper to"'light, treating the exposed paper with an alkaline solution ofpotassium ferrocyanide and sodiumsulfite, and then treating said paperwitha solution of postassium dichromate.

9. A process of blueprinti-ng, which comprises exposing paperphotosensitized with a light-sensitive ferric salt and a ferricyanidecompound to light modified by a design, treating the exposed paper withan alkaline solution containing a ferrocyanide compound, and thentreating said paper with a solution of postassium dichromate.

In testimony whereof I have hereunto subscribed my name.

: ROBERT E. KWECH.

